Place sugar and water in a glass measuring cup. Microwave on high for 30 seconds. Stir well and microwave for another 20 seconds. Stir until sugar is melted. Let cool completely and then refrigerate until needed. Note: This step can be done a day in advance.
Add frozen peach slices, tequila, lime juice, Triple Sec, ice and ⅓ cup simple syrup to a blender. Puree until smooth.
Taste test and add a little more simple syrup if not sweet enough.
Run a lime wedge around the rims of glasses. Pour coarse salt or sugar into a shallow bowl or plate. Dip glass rims in salt.
Pour Margarita mixture into glasses.
